django order_by不在服务器上工作，但在本地机器上工作正常

i have a requests model

我有一个请求模型

class Leave(models.Model):
 from_date = models.DateField(verbose_name='From')
 to_date = models.DateField(verbose_name='To')
 leave_type = models.ForeignKey(TotalLeave,verbose_name='Type',null=True)
 message = models.CharField(max_length=1000,verbose_name='Message to your Manager regarding your leave',null=True)
 created_by = models.ForeignKey(User,related_name='created_user',null=True)
 created_datetime = models.DateTimeField(null=True,blank=True)
 last_modified_by = models.ForeignKey('auth.user',null=True)
 last_modified_date = models.DateTimeField(default=datetime.now,null=True)
 emp = models.ForeignKey('Employee',null=True)
 approval_status = models.BooleanField(default=False,verbose_name='Leaves approved or not ?')
class Lea